Wood panel fabrication using processed wood products (e.g., furnish, wood flakes, raw material) involves steps of drying the wood product, combining and mixing constituent materials (i.e., wood product, resin, wax and scavenging agents), then pressing the materials into a panel. The output is wood panel (i.e., particle board, plywood, oriented strand board, medium density fiberboard).
During the wood product drying operation, byproducts, including wood ash, fibers, semi-solids, and liquids are generated. Such materials are captured by an air pollution control system and collected in a recycling water stream. The liquids and semisolids include hydrocarbons and other organic molecules. In one known process, byproduct gasses are first conditioned with water sprays to achieve adiabatic saturation. As a result, the gas is cooled to the necessary level for hydrocarbon vapors to condense. The fibers, semi-solids and liquids, including hydrocarbon droplets, then are collected by a precipitator and discharged into a recycling water stream. The FIGURE shows a block diagram of a flush water recycling system 10. Included in the FIGURE is a wet electrostatic precipitator 13, also described in U.S. Pat. No. 4,194,888. Recycled water from the settling tank 26 is sprayed via pump 28 into the chamber 24 conditioning and cooling the gas stream to achieve adiabatic saturation. Spray nozzles with a large orifice diameter quench the gas stream by producing large diameter droplets. Such large droplets are unlikely to evaporate completely, thereby creating spray-dried particulate. The large nozzles also are less likely to clog. The spent quench water is drained to the settling tank 26 for treatment and disposal.
Typically, the solids accumulated in the settling tank 26, then are removed by surface skimmers, bottom drag chains, aeration/flotation devices, or filters. Due to the large percentage of liquid material captured with the solids, waste disposal is difficult. The collected waste typically is disposed of by burning in a wet burner or boiler, or by storage in a landfill. Transporting the waste and storing the waste in a landfill is difficult when the waste includes liquid (i.e., 75% to 85% by weight). Accordingly, there is a need to find clean functional uses for the by-product and to reduce the portions discarded as waste.
Another problem with conventional water treatment systems used for wood panel fabrication processes is that the hydrocarbons tend to stay in solution. Previously, the hydrocarbons have been removed from the water treatment system by disposing of the waste water at rates of several gallons per minute. Simple disposal of such water is undesirable. Further, government regulations for discharging waste water are becoming more restrictive. Accordingly, there is a need to reduce the hydrocarbons in solution within the recycling water stream and a need to achieve higher concentrations of solids thereby reducing the volume of material and making handling of the material easier.